To be fair (and I am NO Cardinals fan AT ALL), the Astros were hardly ever a "rival" when they were in the NL Central. They were the perennial punching bag of that division (unless the Brewers extra-sucked in a given year)
"rival" being used in a much more generic sense than what you're thinking of.
but let's look at the rest of your statement.
going all the way back to the realigned divisions in 1994
1994 astros 2nd .5 GB of reds, cards 4th 13 GB
1995 astros 2nd 9 GB of reds, cards 4th 22.5 GB
1996 astros 2nd 6 GB of cards
1997 astros 1st, cards 4th 11 GB
1998 astros 1st, cards 3rd 19 GB
1999 astros 1st, cards 4th 21.5 GB
2000 astros 4th 23 GB of cards
2001 astros 1st, cards 1st and lost tiebreaker
2002 astros 2nd, 13 GB of cards
2003 astros 2nd, 1 GB of cubs
2004 astros 2nd, 13 GB of cards, wildcard
2005 astros 2nd, 11 GB of cards, wildcard
2006 astros 2nd, 1.5 GB of cards
2007 astros 4th, 12 GB of cubs, cards 3rd, 7 GB
2008 astros 3rd, 11 GB of cards
astros were on a tear at the end of 2008 until fuck bud selig decided that the astros should play a "home" series against the cubs in milwaukee to make up for lost dates due to hurricane ike. they lost out in the wild card to fuck bud selig's brewers by 3.5 games.
even after uncle drayton decided to sell the franchise, they weren't last and didn't have the absolutely embarassing records for a couple years (2009 pirates were last, 2010 cubs and pirates were worse). 2011 and 12 were bloody abortions, but we're seeing the fruit of that now.
so, yes, the cardinals were clearly the team of the 00s, but to say that the astros were the perennial punching bag of the division is completely wrong.
in short, your memory of the NL central sucks and i think you're probably fuck bud selig himself.